Comparisons of diatoms and fishes as toxic metal bioindicator: a case study of an A-class wetland in northwest Turkey under effect of an intensive paddy cultivation stress.

In this research, diatoms as the first step and fishes as the last step of the food chain were compared as toxic metal accumulation bioindicator in an A-class wetland in Turkey. Bioaccumulations of potentially toxic elements (PTEs) were determined in liver, gill and muscle tissues of two commercially consumed fish species Carassius gibelio and Cyprinus carpio and in frustules of epiphytic diatom communities living on submerged macrophytes. Samples were collected seasonally from the Gala Lake, which is among the best stopover habitats of birds migrating between Europe and Africa, considering the paddy harvest period that is a major stress factor for the ecosystem. Also, potential human health risks associated with the consumption of fishes and consumption - dermal contact of diatoms were evaluated both for summer - before paddy harvest (BPH) and autumn - after paddy harvest (APH) periods. As a result of this research, the investigated toxic metal concentrations were increased significantly in diatoms in the APH period, while less significant exchanges were recorded in fishes. The bioaccumulations of PTEs were ranked as follows: Zn > Mn > Se > Cu > B > Cr > Ni > As > Pb > Cd for C. gibelio; Zn > Mn > Se > Cu > B > Cr > As > Ni > Pb > Cd for C. carpio; and Mn > Zn > Se > Pb > B > Ni > Cr > Cu > As > Cd for diatom frustules. Although the HI values in diatoms detected in the APH period were statistically significantly higher (about 1000 times; p < 0.05) than detected in the BPH period, they were less than the limit of 1 in both seasons. However, the HI coefficients of fishes were quite higher than the limit (an average of 23.59 for C. gibelio and 19.18 for C. carpio), which means quite high probable non-carcinogenic health risks for humans. Furthermore, the CR coefficients of Cr, Ni and As in muscle tissues of fishes were considerably higher than the limit of 10 -4 , which reflects a significant carcinogenic health risk for consumers. The data showed that although the fishes at the top of the food chain bioaccumulate the PTEs in their tissues much higher than the diatoms at the bottom of the food chain, the diatoms are much more sensitive to changes in the environmental conditions than the fishes and they are more effective biological tools as toxic metal accumulation bioindicators.